JPH0668809A - Color picture tube - Google Patents

Abstract

PURPOSE: To provide a shadow mask type color image tube which reduces moires. CONSTITUTION: A color image tube is provided with an observation screen, a shadow mask 24 arranged adjacently to this screen, and an electronic gun for generating a plurality of electron beams and pointing them to the screen through the mask. The mask has a rectangular peripheral edge with short sides and long sides, and its major axis and minor axis respectively pass the center of the mask and are extended in parallel to the long sides and short sides. The mask has slit-like openings 36, arranged in basically parallel rows to the minor axis, and the adjacent openings 36 in each row are separated by a tie bar 38. The beams scan the screen, while describing scanning lines parallel to the major axis. The length (h) of the opening, as measured in a minor axis direction is almost equal to a multiple of the distance TS between the center of the adjacent scanning lines in the minor axis direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has slit-shaped openings formed by arranging the openings in rows, and the openings in each row are separated by a tie bar. Color video tube of the type having a shadow mask as described above, and in particular, a color video tube having a shadow mask whose aperture length is selected so as to obtain optimum moire performance on the viewing screen of the video tube. It is about.

[0002]

BACKGROUND OF THE INVENTION The majority of color picture tubes in use today include line screens and shadow masks having slit-shaped apertures. The apertures are arranged in rows, with the apertures in each row separated by a web or tie bar in the mask. Such tie bars are essential for maintaining their integrity when the mask is shaped into a dome shape that is somewhat parallel to the shape of the inner surface of the viewing faceplate of the tube. The bars in one row are offset from the tie bars in the adjacent row in the lengthwise direction of the row (ie, the vertical direction). When the electron beam hits the shadow mask, the tie bar blocks part of the beam and creates a shadow on the screen directly behind the tie bar.

When the electron beam is repeatedly scanned in a direction perpendicular to the row of apertures (ie, in the horizontal direction), the scanning produces a series of bright and dark horizontal lines on the screen. These bright and dark horizontal lines interact with the shadows formed by the tie bars to form lighter and darker areas, creating a wavy pattern called a moire pattern on the screen. I can. Such a moire pattern deteriorates the image quality of the image displayed on the screen.

It is highly desirable to select a moire mode that minimizes a moire pattern under all scanning conditions in a television receiver. The two scanning conditions currently used are interlaced scanning and non-interlaced scanning. Moire mode is the ratio of the scan line pitch to the pitch of the shadow formed by the tie bars. Due to practical limits on light output and mask intensity, this moire mode is typically chosen between 6/8 and 10/8. The most selected moire mode is 7/8
Is. Such a mode can be expressed by the following equation. In Mowaremodo = T _s / a _v this equation, T _s is the pitch or period of the scan line of a given television system, which is the height H of the vertical viewing screen of the television system
Is divided by the number of effective scan lines n _e . Also, a
_v is the vertical repeating distance of the mask openings on the screen.

There is also the possibility of using a third scanning condition. This third condition is called progressive scanning and is used, for example, in high definition television receivers. A high scanning frequency is required for progressive scanning. In this special case of progressive scanning, it is considered that only one scanning condition can minimize the moire pattern. Under this scanning condition, a smooth screen can be obtained with less moire. This condition includes:
Moire modes less than 6/8 or moire modes greater than 10/8 may be used. The moire mode most often selected for this condition is 5/8.

Many techniques have been proposed to reduce the problem of moire. Many such techniques involve rearranging the position of the tie bars in the mask to reduce the likelihood of beats between the electron beam scan lines and the shadows of the tie bars. Many of these techniques have been successful in reducing moire so far, but most of these conventional techniques do not correct moire in all parts of the screen, so improved moire reduction has been improved. There is still a demand for technology. What is particularly needed for such improved moire reduction techniques is the new high quality color picture tube required for high definition television. For example, if the performance of electron guns is improved to meet the demands of high definition television,
The electron beam spot formed on the screen by such an improved electron gun becomes smaller. Smaller electron beam spot sizes produce visually sharper scan lines on the screen, and such scan lines interact with the tie bar shadows, further exacerbating the moire pattern problem.

[0007]

SUMMARY OF THE INVENTION An improved color picture tube in accordance with the present invention includes a viewing screen, a shadow mask disposed adjacent the screen, and a plurality of electron beams which are projected through the mask onto the screen. It is equipped with an electron gun. The mask has a rectangular periphery with two long sides and two short sides. The long axis passes through the center of the mask and extends parallel to the long side, and the short axis passes through the center of the mask and extends parallel to the short side. The mask has slit-shaped apertures arranged in rows extending substantially parallel to the short sides. Adjacent apertures in each row are separated by tie bars in the mask. The beam can scan the screen to describe a scan line parallel to the long axis. An improvement of the invention is that the length of the aperture measured in the direction of the minor axis is approximately equal to a multiple of the center-to-center distance between adjacent scan lines measured in the direction of the minor axis.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a rectangular color picture tube 10 having a glass envelope 11 including a rectangular faceplate panel 12 and a tubular neck 14 connected by a rectangular funnel 15. Funnel 15 is an internal conductive coating (not shown) that extends from anode button 16 to neck 14.
have. Panel 12 is an observation face plate 18
And a peripheral flange or sidewall 20 sealed to the funnel 15 by a glass frit 17. A three-color phosphor screen 22 is supported on the inner surface of the face plate 18. Screen 22 is a line screen having phosphor lines arranged in triads, each triad containing phosphor lines for each of the three colors.

A porous color selection electrode, or shadow mask 24, is removably mounted by conventional means in a predetermined relationship at a distance from the screen 22. In addition, an electron gun 2 schematically shown by a dotted line in FIG.
6 is mounted centered in the neck 14 and produces three electron beams 28 which direct these beams through the mask 24 along a concentric path through the screen 2.
Project to 2.

The tube of FIG. 1 is an external magnetic deflection yoke, eg,
It is designed for use with the yoke 30 shown near the funnel-neck junction. When energized, the yoke 30 directs the three beams 28 onto the screen 22.
Place it under the influence of a magnetic field that causes the beam to scan horizontally and vertically so as to draw a rectangular raster on it. The initial plane of deflection (at the time of zero deflection) is almost in the middle of the yoke 30. Due to the fringe magnetic field, the deflection region of the tube is axially moved from the yoke 30 to the gun 2
It extends in the area of 6. For simplicity of illustration, the actual curvature of the deflected beam path in the deflection region is not shown in FIG.

The shadow mask 24 forms a part of the mask-frame structure 32.
Further includes a peripheral flange 34. This mask
The frame structure 32 is shown disposed in the faceplate panel 12 in FIG. Shadow mask 24
Includes a curved perforated portion 25, an unperforated border 27 surrounding the perforated portion 25, and a skirt portion 29 that is bent rearward from the border 27 and extends away from the screen 22. The mask 24 is fitted inside or outside the frame 34, and the skirt portion 29 is welded to the frame 34.

The shadow mask 24 shown in detail in FIGS. 2 and 3 has a rectangular peripheral edge having two long sides and two short sides. Further, the mask 24 has a long axis X that passes through the center of the mask and is parallel to the long side, and a short axis Y that also passes through the center of the mask and is parallel to the short side. The mask 24 includes slit-shaped apertures 36 arranged in rows 37 essentially parallel to the minor axis Y. Adjacent apertures 36 in each row are separated by tie bars 38 in the mask. Figure 3
As shown in FIG. 5, the interval between adjacent tie bars 38 in the row is the tie bar pitch at a specific position on the mask, or the vertical repetition a _v . The length of the aperture is represented by h.

The method of making the shadow mask 24 includes making a flat mask with apertures that will later be formed into a dome-shaped mask. A tube constructed in accordance with the method of the present invention utilizes the relationship that minimizes moire between the slit aperture length h and the electron beam scan line pitch T _s . Such a relationship is determined as follows.

The electron beam energy passing through the illustrated mask aperture array is a periodic function of the vertical position y integrated in the horizontal direction x within the aperture array interval T _x as shown in the following equation (1). Is.

[Equation 1]

The beam energy E _M (y) has a vertical period T _Y equal to the vertical pitch a _v of the mask openings. This beam energy E _M (y) can be represented by the following equation (2) by the distributed Fourier series.

[Equation 2] Where J = (− 1) ^1/2 ; n = coordinates of points in y direction within pitch a _v ; N = total number of sampling points n used to define pitch a _v ; X _M (k) = It is a k-th order Fourier coefficient.

The equation (2) can be rewritten as the following equation (3) to obtain the Fourier coefficient X _M (k).

[Equation 3]

FIGS. 4 and 5 show one electron beam scan line 40 as it scans across the mask in the x-direction. The energy distribution within the scan line 40 is shown in FIG. 4 as a series of points and in FIG. 5 at one point in an enlarged scale. This energy distribution is somewhat bell-shaped, with the intensity peak located approximately in the center of the scan line. The mask is scanned with a similar series of scan lines parallel to the one shown.

Considering a uniform scan line of constant intensity, such as scan line 40 shown in FIG. 4, three consecutive adjacent scan lines have energy distribution 41, as shown in FIG. Some of 42 and 43 overlap each other. When these three energy distributions are added, a composite energy distribution 44 having a modulation factor m defined by the following equation (4) is obtained.

[Equation 4] Here, I _MAX and I _MIN are the maximum intensity and the minimum intensity, respectively. The combined energy distribution 44 exhibits periodicity in the y direction.

FIG. 7 shows a special composite energy distribution 45.
Shows the case where the modulation factor m is very large. Such an energy distribution is obtained, for example, when using a high quality electron gun with a very finely focused electron beam. This large modulation factor m gives the most critical condition for the large Moire effect on the screen of the tube to appear.

Since all periodic functions can be expressed as the sum of sine and cosine functions, the energy distribution s (n) in the y direction can be considered to be the cosine function at the sampling point n. Here, the sampling point n is
There are a total of N pieces, which belong to one line in the y direction. That is,

[Equation 5] In this equation (5), a is the average intensity value of the television signal, m is the modulation factor, w _s is the pulse frequency of the signal in the y direction, and the corresponding spatial period is T _s = 2π / w _s. ,
φ is a phase value.

By superimposing two periodic effects, that is, the periodic energy transmission characteristic E _M (n) of the mask and the energy distribution s (n) of the television signal, the equation (6) is obtained.

[Equation 6]

FIG. 8 shows a typical mask transmission pattern seen vertically along one row of apertures. The apertures allow the beam to pass and the tie bars prevent the beam from passing. The peak-to-peak distance in FIG. 8 is the tie bar pitch a _v described above.

FIG. 9 shows a typical vertical y-direction cross section of a uniform television signal scan line along an array of apertures. The peak-to-peak distance in FIG. 9 is the center-to-center distance T _s between scanning lines.

FIG. 10 shows the electron beam energy passing through a row of apertures viewed vertically. From the figure, it can be seen that some electron beam energy is blocked by each of the tie bars in the mask.

FIG. 11 shows the electron beam energy which has passed through the row of apertures adjacent to the row of apertures shown in FIG. Figure 10
11 is compared with FIG. 11, it can be seen that the vertical position at which the energy passing therethrough is maximized in the adjacent aperture rows.

For a given mask structure period T _y , the Moire effect is a function of the period T _s of the television signal and the phase φ. The purpose of minimizing the Moire effect can be achieved by finding T _s so that the energy passing through the mask and transmitted by each mask aperture is not influenced by the phase φ of the television signal.
In such a case, the position of the scan line of the television signal with respect to the mask aperture has no effect on the transmitted energy or transmitted energy.

In order to calculate the energy passing through each individual mask aperture, one must consider the integral of the function shown in equation (7) over period T _y .

[Equation 7] E for phi (w _s, phi) by using a derivative of, can be obtained w _s to minimize energy from the following equation (8).

[Equation 8]

Since the derivative in equation (8) is still a function of the phase φ, its independent variable (argumen)
It becomes 0 only when the absolute value (modulus) of t) is 0. The absolute value of this independent variable is the product | X _M (k) || sin
It is given by the sum of (w _s + φ) |. However, | s
in (w _s + φ) | is a frequency f _s equal to w _s / 2π
Is only equal to either 0 or 1. Therefore, in the sum of | X _M (k) || sin (w _s + φ) |, a value | X _M (k) corresponding to the frequency f _s = w _s / 2π
Only | must be considered. Equation (8), that is, the purpose of minimizing the sum of the products | X _M (k) || sin (w _s + φ) | is that the value of f _s = w _s / 2π is | X _M (k) | Achieved when selected to be minimum or zero.

For a perfectly rectangular mask aperture, the absolute value is 0 when the aperture length h is equal to or a multiple of the scan line period T _s . Therefore, the aperture length h that minimizes the Moire effect can be expressed by the following equation (9) when expressed using the period T _s = 2π / w _s . h = multiple of T _s , or preferably T _s (9)

As mentioned above, T _s is equal to the vertical height of the screen divided by the number of effective scan lines on the screen. For example, for a television signal with 625 scan lines, T _s = H / 550.

FIG. 12 shows the vertical length h of the aperture with respect to T _s .
Absolute value of the Fourier coefficient with respect to the ratio (the height of the observation screen divided by the number of effective scanning lines on the screen) |
6 is a graph showing the modulation of light passing through an aperture, represented by X _M (k) |. The ratio of h to T _s has the same value on the formed mask surface and on the entire panel surface.

When the corner portion of the mask opening is not made into a right angle, the Fourier opening coefficient X _M (k) can be used to calculate the mask opening structure having an actual roundness. By considering X _M (k) for the actual mask structure, selection of T _s, as shown in FIG. 13, by matching the 1 / T _s to the minimum value of the absolute value of X _M (k) Done. That is, for a given mask having a given pattern, when the end of the slit-shaped opening is at a right angle, an appropriate period T that is equal to the opening length h of the slit-shaped mask opening is obtained. _{If s} is chosen and the ends of the apertures are not squared, the value of T _s will be somewhat different.

FIG. 14 is a graph showing the aperture length in the upper right quadrant of the shaped shadow mask formed according to the present invention. This mask has a diagonal dimension of 86 cm and 16:
Used for tubes with screens with aspect ratio of 9. In this graph, contour lines indicate the positions of openings having the same length in the mask. Note that FIG.
In 4, all dimensions are in mm.

[Brief description of drawings]

FIG. 1 is a sectional view along the axis of a color picture tube embodying the present invention.

2 is a rear view of the mask-frame assembly of the tube of FIG. 1. FIG.

3 is an enlarged plan view of a portion of the shadow mask of the tube of FIG.

FIG. 4 is a diagram of one electron beam scanning line showing the intensity distribution at a plurality of points.

FIG. 5 is an enlarged view of the electron beam scanning line of FIG.

FIG. 6 is a diagram showing the intensities of two adjacent electron beam scanning lines and their combined energy distribution.

FIG. 7 is a diagram showing a combined energy distribution similar to that of FIG. 6 when the degree of modulation is large.

FIG. 8 is a diagram showing a typical mask transmission pattern.

FIG. 9 is a diagram showing a cross section along a typical vertical y-direction of a uniform television line.

FIG. 10 is a diagram showing energy along a vertical mask aperture row in a vertical direction.

11 is a diagram showing energy along a row of vertical apertures adjacent to the row of FIG.

FIG. 12 is a diagram showing the modulation degree m with respect to the aperture length-to-scan line spacing ratio.

FIG. 13 is a diagram showing Fourier coefficients X (k) for a mask having right-angled openings at the ends and a mask having rounded openings at the ends.

FIG. 14 is a diagram showing an aperture length distribution in one quadrant of a shadow mask molded according to the present invention.

[Explanation of symbols]

22 screen 24 shadow mask 26 electron gun 36 aperture 38 tie bar h aperture length T _s center-to-center distance between adjacent scan lines

Claims (1)

[Claims] 1. An observation screen, a shadow mask disposed adjacent to the screen, and an electron gun for generating a plurality of electron beams and directing the electron beams to the screen through the masks. The mask has a rectangular periphery having two long sides and two short sides, a long axis extending through the center of the mask and parallel to the long sides, and a short axis passing through the center of the mask and the short sides. Extending parallel to the sides, the mask has slit-shaped apertures arranged in rows essentially parallel to the minor axis, with adjacent apertures in each row separated by tie bars in the mask. Further, the electron beam scans the screen by drawing a scanning line parallel to the long axis, and as a feature, the length of the aperture is measured in the direction of the short axis. Double the distance between the centers of adjacent scan lines Color video tubes, which are almost equal in number.